The use of information technology (e.g., computer systems, etc.) has increased rapidly, and this use has required the storage of large amounts of data, usually in the form of digital data. This digital data includes bank records, Web sites with millions of Web pages, music, and motion pictures, etc. It is often necessary to be able to get access to the data at any time of the data; in other words, it is often necessary that the data be available 24 hours/day, 7 days a week. Further it is often necessary that the data be safeguarded from loss of the data, and thus, backup systems, which keep a backup or archival copy of the data in a safe medium (e.g., optical storage or tape storage), are often used to maintain and preserve the data in case the primary storage device (e.g., hard drives) fail. These requirements (e.g., the storage of large amounts of data which must be available at any time of the data and which must be safe guarded from loss) present difficult challenges for data storage systems which must attempt to safeguard the data (e.g., by archiving backup copies) without disrupting the desire for users to get access. Thus, it is desirable that backup operations, which make backup copies, be performed with minimal disruption to the users. Further, the backup operations should normally be done in a way that leaves the state of the captured data consistent with any ongoing storage processes. This means that all transactions and updates must be completed before the data is captured for the backup.
An example of a transaction is withdrawing money from a bank savings account. If this is performed by a user at an ATM, the account must be identified and the account holder must be verified. The amount of the withdrawal is entered and transaction information is sent to the account database. The withdrawal date, time, and amount information must be recorded and the current balance must be updated. These actions are part of the transaction. The associated data is in a consistent state if the exemplary transaction has been entirely completed or before the transaction has started processing. This means that the savings account information must reflect the new balance and record the withdrawal or not record the withdrawal and reflect the old balance. An example of an inconsistent state would be recording the withdrawal but not updating the new balance.